This project is designed to increase our understanding of cancer cell biology and to develop a new approach to cancer treatment through the study of growth-regulatory signal transduction events. This work is currently focused on (1) novel aspects of the regulation of cancer cell growth by the retinoblastoma susceptibility gene family and (2) the molecular mechanism of negative growth regulation by cyclic AMP. The retinoblastoma protein is currently thought to function only in the cell nucleus and only in the G1 phase of the cell cycle. In contrast, using confocal microscopy and co-immunoprecipitation techniques we found that Rb is associated with the cell cytoskeleton and that this localization is regulated as a function of the cell cycle. These data were supported by in vitro transcription-translation experiments using wild type and mutant GST-Rb constructs, and by transient transfections using hemagglutinin-tagged wild type and mutant Rb constructs. These data suggest a new model of tumor suppressor gene function, in which the tumor suppressor gene product is responsive to cell-cell or cell-substratum interactions. While studying the anticancer action of cyclic AMP we determined that elevation of intracellular cyclic AMP causes loss of cyclin A expression and down-regulation of cyclin A-regulated cyclin-dependent kinase activity. Our recent studies on the mechanism of cyclic AMP-induced G1 arrest in prostate cancer cells demonstrate that cyclic AMP induces transcription of the cyclin-dependent kinase inhibitor p21. We are mapping the cyclic AMP-responsive element on the p21 promoter and have begun characterizing the factors activating the proximal promoter in response to cyclic AMP. These studies demonstrate that cAMP activates the p21 promoter through a novel, non-CRE-mediated mechanism. Furthermore, the data demonstrate the role of histone acetylases (HATs) in p21 promoter activation in response to cAMP.
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